The present invention relates generally to data transfer systems, and more particularly to a method for sending data in a connectionless manner in a network which supports connection-oriented communications.
Connection-oriented networks are traditionally associated with telephony and other types of communications where an association between a sender and receiver exists for a relatively long period of time (i.e., on the order of minutes). Connection-oriented communications are used when resources need to be assigned to guarantee that the data is received and processed by the proper destination terminal. Connection-oriented communications are typically used for data which is sensitive to delay and/or delay variation. Many networks which support connection-oriented communications use the Asynchronous Transfer Mode (ATM) protocol for data message transfers because it is a relatively fast, highly reliable switching protocol. A more detailed discussion of the ATM protocol can be found in CCITT, "Draft Recommendation I.363." CCITT Study Group XVIII, Geneva, Jan. 19-29, 1993.
The process of exchanging information on a connection-oriented network usually requires some signaling between the source and destination (and possibly a network manager) to negotiate the parameters of the connection before any useful data is exchanged. This is efficient when the delay required for signaling is small relative to the duration of the time spent to exchange information.
In contrast, connectionless networks such as the global Internet, are traditionally associated with computer networks and other types of communications where an association between a sender and receiver exists on a per-packet basis (i.e., on the order of milliseconds). Connectionless communication networks do not utilize advance signaling before sending data; therefore, there is no opportunity for the network to evaluate whether a given transmission can be guaranteed to reach its destination in a timely manner. Connectionless communications are typically used for lower priority data, such as Internet Protocol (IP) data, where it is not imperative that data will arrive at and be processed by the proper destination terminal in a timely fashion.
Once a geosynchronous satellite is introduced into the path between the source and destination or between the source and the network manager, the cost in delay of performing connection-oriented communications is exacerbated. For connection-oriented communications over a satellite with an on-board cell relay switch, to establish a communications link between a source terminal and a destination terminal, the following setup procedure steps need to be conducted:
a) A request is sent from the source terminal over the satellite to the Network Operations Center (NOC) asking for a connection identification address (CID) for a connection to the destination terminal and a channel for communications.
b) A channel, a CID and a path through the satellite cell switch are allocated by the NOC.
c) The channel allocation, CID, and path through the satellite cell switch are sent to the satellite.
d) The channel allocation and CID are sent to both the source terminal and the destination terminal.
Although this set-up procedure requires a significant amount of time, it accomplishes many purposes the most significant of which is that a path from a satellite uplink to a satellite downlink is created through the satellite network for the routing of cells with the header CID. In addition, the source terminal will know that it can use the allocated channel for communication with the desired destination terminal; the desired destination terminal will listen only to the allocated channel and accept only the packets with the proper CID in the header; and, other destination terminals do not use their resources to accept packets not intended for their use freeing up resources for communications with other source terminals.
After the set-up procedure is completed, the following additional steps are performed in order to send a message from the source terminal to the destination terminal:
a) The source terminal divides the message into one or more cells, each of which is of a length compatible with the data message transfer protocol used by the network. For networks which use the ATM protocol, this step is conducted in accordance with a predetermined ATM Adaptation Layer (AAL) protocol. As required by most protocols, each cell includes a header.
b) The source terminal places the allocated CID into the proper location in the header of each cell.
c) The cells are sent to a satellite.
d) Each cell is routed to the downlink antenna which covers the desired destination terminal.
e) The cells are broadcast by the downlink antenna.
f) The cells with the proper CID in the header are accepted by the destination terminal and reassembled back into the original massage.
The CID is an address identifying the connection between a specific source terminal and destination terminal. It is temporary and used for a single communication. After the communication between the source terminal and the destination terminal is complete, the connection is broken and the channel can be reused for another communication either between the same source and destination terminal or a new source and destination terminal. The CID can also be reused for another communication either between the same source and the destination terminal, a new source and the destination terminal or a new source and a new destination terminal.
In contrast, for connectionless communications, the message is sent from the source terminal to the destination terminal without first completing the set-up portion of the procedure. Sending a message in a connectionless communications networks takes much less set-up time than sending a message in a connection-oriented communications system since the set-up procedure with a NOC or network manager is not required. However, in a connectionless communications system there is no guarantee that the downlink antenna will have the channel capacity available to broadcast the packets to the destination terminal, nor is there a guarantee of resources in the on-board cell switch.
With the advent of the Internet, the demand to transport data in a connectionless manner has increased tremendously. Therefore, it would be advantageous to develop a scheme to send data, such as IP data, in a connectionless manner over a system which supports connection-oriented communications. It would also be advantageous to do so in a manner which is compatible with the ATM protocol used in many connection oriented systems.
U.S. Pat. Nos. 5,432,777 and 5,517,497 disclose a method for sending data in a connectionless manner over a connection-oriented network which includes assigning a routing identifier (RI) to each terminal in the network and placing a destination terminal RI in the header of each cell of the message. For this method, the source terminal consults a global look-up table which correlates each terminal in the system with an RI in a unique mapping arrangement. The source terminal places the destination terminal RI in the header of each cell. The cells are sent to a node in the system. Each node must read the destination terminal RI in the header of each cell and determine the proper routing sequence required for the cells to be transmitted to the proper destination terminal.
The cells are routed through each satellite to the desired destination terminal. The destination terminal only accepts cells having its individual destination terminal RI in the headers. After the data is routed to the proper destination terminal, the destination terminal typically must separate, or demultiplex, the cells since cells sent from different source terminals are multiplexed together before arriving at the destination terminal. To separate multiple streams of data coming from different source terminals to the same destination terminal, the '777 and '497 patents disclose using a multiplexing identification (MID) field in the cell headers where the value of the MID field allows, at the destination side, to identify the cells which belong to the same connectionless message. This value has to be unique. The '777 and '497 patents prefer that the source RI value be used as the MID and either the last ten bits of the RI value are taken as the MID or, the header is extended to allow more bits to be used. Using the MID field to demultiplex cells from different sources restricts the ATM Adaptation Layer (AAL) protocol which can be used to demultiplex the cells to the ATM Adaptation Layer 3/4 (AAL3/4) protocol. A more detailed discussion of AAL protocols can be found in CCITT, "Draft Recommendation I.363." CCITT Study Group XVIII, Geneva, Jan. 19-29, 1993. The AAL3/4 protocol has a MID field, but, the newer ATM Adaptation Layer 5 (AAL5) protocol does not. Therefore, the method specified in the '777 and '497 patents does not support the newer AAL5 protocol which is typically the adaptation layer protocol of choice for IP data transfers among those skilled in the art. Thus, the scheme defined in the '777 and '497 patents are deficient for various network environments.
In co-pending application Ser. No. 09/262,890, filed Mar. 10, 1999, a method was detailed to solve the inadequacies of the prior art. This method assigned unique beam identifiers to each downlink antenna beam in the network and mapped the destination terminal address of the selected destination terminal to a beam identifier indicating which antenna beam covered the selected destination terminal. The beam identifier was placed in the header of each cell of the message and was used to route the cells to the proper downlink antenna.
The step of mapping the destination terminal address to a downlink beam identifier requires a separate look-up table at each source terminal which correlates destination terminal addresses to downlink beam identifiers. This table requires resources in the network to generate and maintain the look-up tables. What is needed is a method for sending data in a connectionless manner over a network which supports connection-oriented communications in which the method does not require a separate look-up table correlating destination terminal addresses to downlink beam identifiers.